1. Field of the Invention
The present invention relates, in general, to granulocytic Ehrlichia. In particular, the present invention relates to a cell line selected from the group consisting of a promyelocytic leukemia cell line, an acute myelogenous leukemia cell line, a histiocytic lymphoma cell line, a monocyte macrophage-like cell line, an acute monocytic leukemia cell line, and an embryonic lung cell line wherein the cell line is infected with granulocytic Ehrlichia, a method of continually growing granulocytic Ehrlichia, vaccines comprising granulocytic Ehrlichia or granulocytic Ehrlichia antigens, methods of preventing ehrlichiosis in an animal, antibodies to granulocytic Ehrlichia, and methods for detecting granulocytic Ehrlichia or antibodies to granulocytic Ehrlichia in an animal.
2. Related Art
A wide range of virus, bacteria and parasites are transmitted to mammals by ticks. In the United States, Lyme disease is the most frequently reported tick borne disease. The etiologic agent of Lyme disease, B. burgdorferi, is transmitted by ticks of the genus Ixodes (Mather et al., JAVMA 205:186-188 (1994)).
Another tick borne disease, ehrlichiosis, is caused by the genera of bacteria known as Ehrlichia (for review of Ehrlichia and Ehrlichia diseases see, Rikihisa, Clin. Microbiol. Reviews 4(3):286-308 (1991)). The various species of Ehrlichia are all members of the family of Rickettsiaceae. Unlike B. burgdorferi, Ehrlichia do not require a mammalian host to maintain themselves in the wild. However, if a mammalian host is involved, most Ehrlichia species infect monocytes of the blood and in several cases have been isolated in monocyte cell culture (see, for example, Dawson et al., U.S. Pat. No. 5,192,679 issued Mar. 9, 1993 which claims a canine monocyte macrophage cell line DH82 infected with E. canis).
Ehrlichia equi is the causative agent of equine ehrlichiosis (Rikihisa, Clin. Microbiol. Reviews 4(3):286-308 (1991)). Although the transmission mechanism has not been defined, it appears to be unusual in that it infects granulocytes and not monocytes. E. equi has a broad range of hosts. Experimental infection of horses, burros, sheep goats, dogs, cats, monkeys, and baboons has been reported (Lewis, Vet. Parasitol. 2:61-74 (1976)). In Europe, another granulocytic Ehrlichia, E. phagocytophila, causes tick borne fever in sheep, cattle, and bison, and is vectored by I. ricinis (Ristic, M. et al., in Bergey's Manual of Systemic Bacteriology, Kreig, N. et al., eds., Williams and Wilkins, Baltimore (1984), pp. 704-709). Although these organisms are carried by different ticks and are reported on different continents, they are indistinguishable from one another by serologic or PCR methods (Chen et al., J. Clin. Microbiol. 32:589-595 (1994)). Recently, several fatal cases of human granulocytic Ehrlichosis have been reported in Wisconsin, Minnesota, and Connecticut as well as a non-fatal human case in Florida (Chen et al., J. Clin. Microbiol. 32:589-595 (1994)). These cases of ehrlichiosis were caused by an Ehrlichia that was indistinguishable from E. equi and E. phagocytophila by PCR methods (Bakken, J. S. et al., JAMA 272:212-218 (1994); Rynkiewicz and Liu, New Engl. J. Med. 330:292-293 (1994)).